1. Field of the Invention
The invention relates generally to water treatment polymers and, more particularly, the invention relates to anionic polymers useful as flocculants and methods of preparing and using the same.
2. Description of Related Technology
Considerable expenditures are made each year for materials used in water treatment, such as flocculants and coagulants used to clarify raw waters for potable and industrial use. Flocculants are used to clarify municipal and industrial effluents to remove pollutants and to improve the efficiency of papermaking processes by increasing the first pass retention of fiber and filler when paper is formed on a paper machine and for other process clarification needs. Therefore, the demand for more efficient, inexpensive water treatment compositions for use as flocculants is increasing.
Anionic high molecular weight polymers are widely used as flocculants to clarify waters for potable and industrial use. Some commercially available anionic polymers include pendant carboxyl units connected to a backbone chain. These units function as active sites for linking with solid particles suspended in the water to be treated. The active carboxyl units along the chain begin to become deprotonated at about pH 4.6 and deprotonation increases as pH increases. Accordingly, the deprotonated sites become anionic, exhibiting a single negative charge per carboxyl pendant. In the flocculant-type applications described above, it would therefore be advantageous to increase the negative charges per active pendant unit to increase polymer activity and efficiency.
In water stabilization applications, the use of phosphono-methylated amine compounds to sequester polyvalent metal ions, especially calcium and magnesium, has been the subject of investigation for many years. It has been found that four phosphono units can be attached to a diamine base while five phosphono units may be attached to a triamine base to provide additional sequestering ability. Amine-based phosphonates have enjoyed commercial success as sequesterants and chelating agents in industrial systems needing control over such metal ions as calcium, magnesium, iron, and manganese.
In the past, a Mannich-type reaction has been used to prepare phosphono-methylated amines using phosphorous acid, formaldehyde and ammonia or amine compounds. See Moedritzer & Irani, J. Org. Chem., 31, 1603-1607 (1966). It has also been disclosed that certain polymers containing phosphonate units may be copolymerized with other materials such as acrylamide, acrylic acid and acrylates to produce scale and corrosion inhibitors for water systems such as cooling, boiler and gas scrubbing systems. See Becker, U.S. Pat. No. 4,446,028 (May 1, 1984) and Hoots et al., U.S. Pat. No. 4,904,413 (Feb. 27, 1990).